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Question

Let u=^i+^j,v=^i^j and w=^i+2^j+3^k. If ^n is a unit vector such that u.^n=0 and v^n=0, then |w^n| is equal to:

A
1
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B
2
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C
3
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D
0
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Solution

The correct option is D 3
Let ^n=x^i+y^j+z^k, where x2+y2+z2=1.
Now, u.^n=0(^i+^j).(x^i+y^j+z^k)=0x+y=0(1)
Also, v.^n=0(^i^j).(x^i+y^j+z^k)=0xy=0(2)
Solving (1) and (2), we get x=y=0. Thus z=1or1 (because x2+y2+z2=1
Thus, w.^n=(^i+2^j+3^k).(±^k)=±3

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